Vitamin E can prevent damage in smolts
Farmed salmon need vitamin E in all life stages, but especially when smoltifying to ensure good health, says Pauline Wischhusen of Norway's Institute of Marine Research.
During the smoltification phase, farmed salmon need feed with added vitamin E to avoid eye damage and spinal deformities, according to new research from Norway's Institute of Marine Research (IMR).
“Vitamin E helps protect the salmon's eyes, skeleton, organs and blood. It makes the smolt better equipped to handle the conditions it encounters in the sea,” says Wischhusen.
New feed recipes
Over several months at IMR’s research station in Matre, researchers have followed Atlantic salmon fed experimental diets.
In recent years, commercial salmon feed has changed a lot. Marine ingredients such as fishmeal and fish oil are used less, and synthetic antioxidants are increasingly being replaced by natural antioxidants.
More knowledge is needed about which micronutrients salmon need at different stages of their life. This information could enable a shift towards more precise feeding that can give the fish what they need, when they need it.
“When salmon smolt, they need some key nutrients, including vitamin E. These substances make the fish better equipped to handle the conditions it encounters in the sea” says Wischhusen.
She leads the FHF-funded project Revitalise, which investigates the salmon’s need for multiple micronutrients.
Tested seven different diets
The IMR researchers have investigated the effects of a total of seven diets with different levels of vitamin E.
The lowest amount of vitamin E was 38 mg/kg. This corresponds to a feed without additional added vitamin E, with only the vitamin content that naturally comes from the ingredients.
The highest amount was 710 mg/kg. This is the highest level of vitamin E recorded in commercial salmon feed in IMR’s monitoring programme in 2022.
The project leader describes that salmon fed the lowest levels of vitamin E had greater challenges.
“This group had more cataracts than smolts in seawater, and more of the same specific type of vertebral deformity in the immediate aftermath.”
According to IMR, salmon need feed containing at least around 82 mg/kg of vitamin E while smoltifying to avoid these risks.
In the feed monitoring programme, IMR has found that commercial feed in 2026 contains a minimum level of approximately 184 mg/kg of vitamin E.
“Today’s feeding practices should therefore be sufficient to prevent these welfare problems,” says Wischhusen.
The results have recently been published in the journal Aquaculture Nutrition.
Higher levels provide more health benefits
The researchers have monitored and sampled the fish throughout the entire experiment, from smolt to five months into the sea phase.
The results showed that an even higher level of vitamin E can provide better protection of tissue and blood, especially when the salmon are exposed to stress.
“When we looked at tissue wear, how much vitamin E is stored in the liver, the fish’s blood values and muscle pigment, the results indicated that a range of 367-450 mg/kg provided better protection for the salmon.”
Slight variations in growth were observed across vitamin E levels.
No negative effects were detected in the fish fed the highest levels of vitamin E. However, the researchers saw signs of accumulation in the liver, suggesting that the fish were not converting the vitamin E as efficiently.
Next step: supplements for sick fish
Some of the experimental fish are being included in a follow-up experiment, where they are infected with PRV-1, a virus that can cause heart and skeletal muscle inflammation.
The purpose is to investigate whether higher vitamin E levels help the fish handle the viral infection better.
“Preliminary results indicate that vitamin E has beneficial effects on disease.”
At the same time, the researchers are conducting a feed trial at a commercial fish farming location to investigate how vitamin E levels affect growth and welfare under real-world conditions.